1. Field of the Invention
The present invention relates to an ink supply system for supplying ink through a connect portion that can be connected and disconnected, an ink jet printing apparatus, an ink container, an ink refilling container and an ink jet cartridge.
2. Description of the Related Art
Among printing apparatus that print an image on a print medium by applying ink from a print head onto a print medium, there is a serial scan type printing apparatus that applies ink from the print head onto the print medium while moving the print head. As the print head an ink jet print head which can eject ink toward the print medium may be used.
In general, the serial scan type printing apparatus using an ink jet print head print an image on a print medium by repetitively alternating two different operations, one that ejects ink from the print head onto the print medium while moving in a main scan direction the print head along with a carriage on which the print head is mounted and the other that feeds the print medium in a subscan direction crossing the main scan direction. The ink that the print head ejects is supplied from an ink tank.
One method of supplying ink to the print head involves mounting a large ink tank along with the print head on the carriage and supplying ink from the large ink tank to the print head. With this method, however, mounting the large ink tank on the carriage increases the weight of the carriage, making it difficult to stably drive the carriage in the main scan direction at high speed and leading to a possible increase in the size of a carriage drive system. Another ink supply method involves installing an ink tank at a predetermined position in the printing apparatus and supplying ink from the ink tank to the print head on the carriage through a flexible tube. This method also has a drawback that variations in carriage moving load and ink supply pressure resulting from deformations of the tube as the carriage moves may degrade a quality of a printed image.
The inventor of this invention previously proposed an apparatus that overcomes such drawbacks (Patent Reference 1).
The previously proposed apparatus has a relatively small subtank mounted on a carriage to supply ink to the print head and has a relatively large main tank installed at a certain position in the printing apparatus, with the ink being supplied from the main tank to the subtank when the carriage reaches a predetermined position. That is, when the carriage moves to the predetermined position, a joint on the main tank side and a joint on the subtank side are connected together to form an ink supply path and an ink recovery path between the main tank and the subtank. Then, the ink is delivered under pressure from the main tank through the ink supply path to the subtank until it overflows the subtank, with the overflowing ink returned along with air in the subtank to the main tank through the ink recovery path. After the subtank is supplied and overflowed with ink, the carriage is moved away from the predetermined position to disconnect the joint of the subtank from the joint of the main tank, thus disrupting the ink supply path and the ink recovery path.
Such a printing apparatus can eliminate drawbacks experienced with the conventional apparatus when a large ink tank is mounted on the carriage and when ink is supplied through a flexible tube.
Patent Reference 2 describes a construction in which two connect portions, first and second connect portions, are used to supply ink from a first ink container installed outside the carriage to a second ink container mounted on the carriage.
In this ink supply system a negative pressure generation mechanism using a capillary tube member is provided on the print head side. During a printing operation, external air (open air) is positively introduced from an atmosphere communication port on the print head side into the second ink container on the print head side. When an ink sensor provided on the print head side detects that a remaining ink in the second ink container is lower than a predetermined level, the carriage moves to a home position where a pump connected to the first connect portion discharges air from the second ink container and at the same time supplies ink from the first ink container connected to the second connect portion into the second ink container. That is, the first connect portion is situated higher in a gravity direction than, and the second connect portion is situated lower than, the second ink container on the carriage. The air in the second ink container is discharged by a suction means such as pump through the first connect portion and a resulting increase in a negative pressure in the second ink container draws ink from the first ink container into the second ink container through the second connect portion for ink refilling.
[Patent Reference 1]
Japanese Patent Application Laid-Open No. 58-194560 (1993)
[Patent Reference 2]
Japanese Patent Application Laying-open No. 2001-138541
With the above-proposed apparatus (Patent Reference 1), however, since the ink is supplied to the subtank until it overflows the subtank, the ink continues to be supplied after the subtank is full. Further, since it is necessary to recover the ink overflowing from the subtank, the printing apparatus is likely to become complex in construction and large in size.
The apparatus of the Patent Reference 2 also uses a suction produced by a pump in supplying ink, so its size may become large. Further, in this apparatus since air is actively introduced into the second ink container on the carriage during printing, when the ink in the second ink container is supplied continuously to the print head in a relatively large volume for printing, the air introduced into the second ink container may be drawn into the print head causing a printing failure. If such a trouble is to be avoided, an installation space between the negative pressure generation mechanism and the print head must be increased to prevent the air taken in from the negative pressure generation mechanism from being drawn into the print head. This puts limitations on their arrangements and sizes.
Further, the air in the second ink container on the carriage expands and contracts due to environmental variations such as ambient temperature and pressure changes causing pressure changes in the second ink container. Positive pressures as a result of pressure changes may cause ink leakage from nozzles of the print head. Conversely, excessive negative pressures may result in an improper ink ejection or a failure to eject ink. Therefore, in the construction of the apparatus of the cited Reference 2, it is necessary to increase the size of the capillary tube member, which also doubles as a buffer, to secure reliability. This hinders a reduction in the size of the print head. Increasing the size of the capillary tube member may lead to an increased size of the print head and a more complicated structure.
Further, if a means to forcibly move a gas out of the second ink container, such as a pump, is not used and particularly if the second ink container on the carriage is a hermetically closed system (i.e., if the second ink container excluding its connect portions for the first ink container and for the print head virtually forms a hermetically closed space), the gas in the second ink container cannot be removed but builds up in the second ink container. When a means such as pump to forcibly move a gas out of the second ink container is not used, even if the ink is supplied intermittently from the first ink container to the second ink container, the gas accumulated in the second ink container cannot be removed and will degrade an efficiency of ink refilling into the second ink container.